In a fixed or mobile wireless Internet Protocol (IP) network, a client-side device establishes a session with a network-side access device to communicate with other entities in that network. The session represents the client-side device to the network, and includes information about the client-side device such as its IP address, location within a mobility area, permitted services and other such attributes required to communicate with the client-side device. The session may be partitioned into separate data elements representing IP connectivity and link-layer connectivity and these data elements may be stored on separate network elements. The session is typically present as long as the client-side device is present in the network, though other resources required for direct communication between the client-side device and the network device may only be in use when active communication is in process.
The state of direct communication between the client-side device and the network-side device is known as a connection. In cellular wireless systems, as the client device must initiate connection, a special procedure known as paging is used to allow the network to request the client device to communicate. For example, if a network device needs to send data to a client device, the network uses the information stored in a session associated with the client device to page the client device. Paging involves transmitting a message addressed to a particular terminal over a shared channel monitored by all terminals in communication with that part of the network. This page causes the client device to initiate a connection with the network, thus enabling an exchange of data. However, if a hardware or software failure of a network-side device causes the network to lose the session information (referred to as a “session breach”), the network cannot establish a direct communication with the client device, as it has lost all knowledge of the device's identity, communication parameters and location required to page that particular device. A session for which session information has been lost due to hardware or software failure of a network-side device is referred to as a “breached session.” Because the session breach is not visible at the IP (Internet Protocol) layer, the client's peers are unaware that the client is unreachable. Thus, network-initiated connection-oriented applications such as online video teleconferencing and Internet telephony are particularly vulnerable to network-side failures. Furthermore, the client device is not immediately aware that the session breach has occurred and its recovery mechanisms operate on a sufficiently long timescale that client-initiated creation of a new session cannot be counted upon to restore network reachability for that client before it is required.